1. Field of the Invention
The present invention relates to a method for operating a drive device of a hybrid vehicle, in particular a hybrid motor vehicle, having at least one internal combustion engine and at least one electric machine, the torques of the internal combustion engine and electric machine being added together.
2. Description of Related Art
Methods of the kind mentioned at the outset are known. To reduce fuel consumption and emissions, the goal is an optimal distribution of the driving torque requested by the driver between the internal combustion engine and the electric machine. The driving torque is divided so that the internal combustion engine is operated in the range of favorable efficiencies and it is possible to charge an electric accumulator belonging to the electric machine. At low driving speeds, however, the internal combustion engine should be turned off and the requested torque should be applied only by the electric machine. In addition, the braking energy in braking of the vehicle may be utilized by recuperation for charging the electric accumulator. Modern gasoline engines having intake manifold injection usually have an electronic throttle valve for regulating the air flow. The accelerator pedal is then decoupled mechanically from the throttle valve. The ultimate setting speed of the throttle valve control element and dynamic charge effects in the intake manifold do not allow a highly dynamic setting of a predefined air flow and of the internal combustion engine torque thereby generated. Electric machines, however, have a much more dynamic response. If the driver requests an increased driving torque, and the internal combustion engine thereby enters ranges of favorable efficiency, the electric machine is usually controlled so that it operates more as a generator. The machines may be triggered in such a way that the negative torque having a higher absolute value coming from the electric machine, which is operated as a generator, is compensated by an increased torque of the internal combustion engine. Due to the fact that, in comparison with the internal combustion engine, the electric machine has a highly dynamic response, the actual driving torque of the vehicle initially declines before approaching the torque requested by the driver. This has a negative effect on drivability and comfort. This undershooting may under some circumstances also excite unwanted vibrations in the drivetrain. To avoid this undershooting, it would be possible to additionally apply the difference between the setpoint torque and the actual torque of the internal combustion engine to the electric machine, to thereby compensate for the delayed torque buildup by the internal combustion engine. In a dynamic style of driving, i.e., with frequent changes in driving torque requirements, the electric machine would be under a highly dynamic load. This would be associated with a highly dynamic electric power demand of the energy accumulator connected to the electric machine, resulting in a high energy conversion in the energy accumulator and shortening its lifetime. In addition, frequent cyclic charging and discharging operations result in high conversion losses, having a deleterious effect on overall efficiency.
In addition, a method for operating the drive device of a hybrid vehicle is known from published German patent document DE 102 01 264. In the case of a negative driving torque demand, the drive unit and a brake system of the hybrid vehicle are triggered in a consumption-optimized manner. The goal in this method is to optimally utilize the available energy of the hybrid vehicle. By recovering braking energy through recuperation in particular, this energy may be fed into the vehicle electrical system, thereby decreasing the fuel consumption of the internal combustion engine.